In wireless communications systems, such as long term evolution (LTE) systems, downlink and uplink transmissions may be organized into two duplex modes: frequency division duplex (FDD) mode and time division duplex (TDD) mode. The FDD mode uses a paired spectrum where the frequency domain is used to separate the uplink (UL) and downlink (DL) transmissions. FIG. 1A is a graphical illustration of an uplink and downlink subframe separated in the frequency domain for the FDD mode. In TDD systems, an unpaired spectrum may be used where both UL and DL are transmitted over the same carrier frequency. The UL and DL are separated in the time domain. FIG. 1B is a graphical illustration of uplink and downlink subframes sharing a carrier frequency in the TDD mode. In LTE-Advanced, carrier aggregation allows expansion of effective bandwidth delivered to a user terminal through concurrent utilization of radio resources across multiple carriers. Multiple component carriers are aggregated to form a larger overall transmission bandwidth. Carrier aggregation may be performed in LTE-Advanced TDD or LTE-Advanced FDD systems.